It doesn’t matter whether you are trying to lose five pounds or more than 50 pounds; all of the same simple laws of physics determine whether or not you will lose weight and how fast your weight loss will occur. While everyone is different, if everyone remembered these simple guidelines and put them into practice, then they would find that these guidelines would generally lead to weight loss without the aid of any special diet plans, books, or medications.
Our weight is determined by the amount of energy that we take in as food, and the amount of energy we expend in the activities of our day. Energy is measured in calories. If your weight remains constant, you are probably taking in the same amount of calories that you are burning each and every day. If you’re slowly gaining weight over time, it is likely that your caloric intake is greater than the number of calories you burn through your daily activities.

Everyone is in control of the amount of food he or she consumes each day, so as a result, our intake of calories is something we can control with relative simplicity. To some degree, we are also able to control our output of energy, or the number of calories we burn each day. The number of calories we burn each day is dependent upon:
1. Our basal metabolic rate (BMR)
2. The number of calories we burn per hour simply by being alive and maintaining bodily functions and
3.

Our level of physical activity
For some people, due to genetic (inherited) factors or other conditions, their resting metabolic rate can be slightly higher or lower than average. Our weight also plays a role in determining how many calories we burn at rest – the more calories that are required to maintain your body in its present state, the greater your body weight. As an example, a person that weighs around a hundred pounds requires less energy (food) to maintain body weight than a person who weighs 200 pounds.
Lifestyle and work habits partially determine how many calories we need each day. Someone whose job involves heavy physical labor will naturally burn more calories in a day than someone who sits at a desk most of the day (a sedentary job). For people who do not have jobs that require intense physical activity, you need exercise or increased physical activity to increase the number of calories burned.
As a rough estimate, an average woman aged 31-50 who leads a sedentary lifestyle needs about 1800 calories per day to maintain a normal weight. A man of the same age requires about 2200 calories. Participating in a moderate level of physical activity (exercising 3-5 days per week) requires about 200 additional calories per day.
In order to lose weight rather than maintain it, you will want to eat sensible, well balanced meals with small portion sizes, cut down or reduce your intake of daily calories, try with your best efforts to eliminate fats from your diet and ensure that you exercise on a regular basis.